Hey I'm looking to add 6 RX480s to my gaming PC when they come out and use them for mining.  My motherboard is a MSI Z77-45 gaming and can accommodate 7 cards.  I currently have a Titan X in one slot that I use for gaming and mining with NiceHash.  I'd like to keep the Titan where it is and add the 6 RX480s on risers.  What PSU should I buy during this upgrade/mod?  Is a platinum 1600 watt overkill?  I'm in CA and have expensive electricity.  Thanks!